Chiral analysis of derivatized amino acids from kefir by gas chromatography

•Analysis of amino acids in kefir samples by chiral gas chromatography was performed.•Several combinations of alkyl chloroformate/alcohols derivatives were synthesized.•Ethyl chloroformate/ethanol mixture lead to the optimum compromise separation/time.•d- and l-proline could be baseline enantioseparated and quantified in kefir samples.

The amino acids present in the kefir samples were derivatized using different alkyl chloroformates combined with alcohols and chromatographed on a (3-O-butanoyl-2,6-di-O-pentyl)-γ-cyclodextrin (Lipodex E) chiral gas–liquid chromatographic column. The combination of derivatization reagents that led to better chromatographic performance for standard amino acid solutions was critically compared. All the chloroformate/alchohol mixtures lead to fast and quantitative reactions. However, the ethyl chloroformate/ethanol mixture was selected since the number of enantioseparated amino acid derivatives was higher. The derivatization was applied to samples of kefir grains grown in raw and in skimmed UHT milk. The samples were previously pretreated by elution from a low-pressure ion-exchange columns. Standard addition calibration curves have been used for the quantitative determinations of amino acid derivatives in both samples, and the figs. of merit of the proposed method have been assessed. The l- and d- configuration of d- and l-alanine, d- and l-valine, d-proline, l-threonine, aspartic and glutamic acids, methionine, and cysteine were detected and quantitatively determined.